U.S. patent application number 12/597496 was filed with the patent office on 2010-06-03 for solar cell and method of fabricating the same.
This patent application is currently assigned to JUSUNG ENGINEERING CO., LTD.. Invention is credited to Jin Hong, Jae-Ho Kim, Yong-Woo Shin.
Application Number | 20100132779 12/597496 |
Document ID | / |
Family ID | 40367152 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100132779 |
Kind Code |
A1 |
Hong; Jin ; et al. |
June 3, 2010 |
SOLAR CELL AND METHOD OF FABRICATING THE SAME
Abstract
A solar cell includes a first electrode on a substrate; a
plurality of pillars on the first electrode; a semiconductor layer
on the first electrode, wherein a surface area of the semiconductor
layer is greater than a surface area of the first electrode; and a
second electrode over the semiconductor layer.
Inventors: |
Hong; Jin; (Gyeonggi-do,
KR) ; Kim; Jae-Ho; (Gyeonggi-do, KR) ; Shin;
Yong-Woo; (Gyeonggi-do, KR) |
Correspondence
Address: |
HOSOON LEE
9600 SW OAK ST. SUITE 525
TIGARD
OR
97223
US
|
Assignee: |
JUSUNG ENGINEERING CO.,
LTD.
Gyeonggi-do
KR
|
Family ID: |
40367152 |
Appl. No.: |
12/597496 |
Filed: |
May 29, 2008 |
PCT Filed: |
May 29, 2008 |
PCT NO: |
PCT/KR08/03010 |
371 Date: |
October 25, 2009 |
Current U.S.
Class: |
136/255 ;
257/E31.039; 257/E31.127; 438/71 |
Current CPC
Class: |
H01L 31/0392 20130101;
Y02E 10/548 20130101; H01L 31/056 20141201; H01L 31/03529 20130101;
H01L 31/035281 20130101; H01L 31/075 20130101; Y02E 10/52
20130101 |
Class at
Publication: |
136/255 ; 438/71;
257/E31.039; 257/E31.127 |
International
Class: |
H01L 31/0352 20060101
H01L031/0352; H01L 31/0232 20060101 H01L031/0232; H01L 31/18
20060101 H01L031/18 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2007 |
KR |
10-2007-0052665 |
Oct 31, 2007 |
KR |
10-2007-0110332 |
Claims
1. A solar cell, comprising: a first electrode on a substrate; a
plurality of pillars on the first electrode; a semiconductor layer
on the first electrode, wherein a surface area of the semiconductor
layer is greater than a surface area of the first electrode; and a
second electrode over the semiconductor layer.
2. The solar cell according to claim 1, wherein the semiconductor
layer includes a first semiconductor layer of a positive type
impurity-doped semiconductor material, a second semiconductor layer
of an intrinsic semiconductor material, and a third semiconductor
layer of a negative type impurity-doped semiconductor material, and
wherein the first semiconductor layer faces the plurality of
pillars, and the second semiconductor layer is disposed between the
first and third semiconductor layers.
3. The solar cell according to claim 2, wherein the substrate is
formed of glass, the first electrode is formed of one of tin oxide
and zinc oxide, and the second electrode is formed of an opaque
metallic material.
4. The solar cell according to claim 2, further comprising a
reflective layer disposed between the third semiconductor layer and
the second electrode.
5. The solar cell according to claim 4, wherein the reflective
layer is formed of zinc oxide.
6. The solar cell according to claim 1, wherein each of the
plurality of pillars includes one of circular shape, an oval shape
and a cross shape.
7. The solar cell according to claim 1, wherein each of the
plurality of pillars has a cross shape having a first axis and a
second axis, and further comprises a connecting line connecting one
end of the first axis of the cross shape and ends of the second
axis of the cross shape has a curved shape.
8. The solar cell according to claim 1, wherein the plurality of
pillars are arranged in a first column and a second column, and
wherein the pillars in the first column and the pillars in the
second columns are alternately arranged.
9. The solar cell according to claim 1, wherein the plurality of
pillars are formed of one of silicon oxide, silicon nitride and a
transparent photosensitive material.
10. A method of fabricating a solar cell, comprising: forming a
first electrode on a substrate; forming a plurality of pillars on
the first electrode; forming a semiconductor layer on the first
electrode, wherein a surface area of the semiconductor layer is
greater than a surface area of the first electrode; and forming a
second electrode over the semiconductor layer.
11. The method according to claim 10, wherein the step of forming
the semiconductor layer includes forming a first semiconductor
layer of a positive type impurity-doped semiconductor material
facing the plurality of pillars, forming a second semiconductor
layer of an intrinsic semiconductor material on the first
semiconductor layer, and forming a third semiconductor layer of a
negative type impurity-doped semiconductor material on the second
semiconductor layer.
12. The method according to claim 11, further comprising forming a
reflective layer between the third semiconductor layer and the
second electrode.
13. A solar cell, comprising: a plurality of pillars on a surface
of a substrate; a first electrode on the surface of the substrate
having the plurality of pillars; a semiconductor layer on the first
electrode, wherein a surface area of the semiconductor layer is
greater than a surface area of the substrate; and a second
electrode over the semiconductor layer.
14. The solar cell according to claim 13, wherein the semiconductor
layer includes a first semiconductor layer of a positive type
impurity-doped semiconductor material, a second semiconductor layer
of an intrinsic semiconductor material, and a third semiconductor
layer of a negative type impurity-doped semiconductor material, and
wherein the first semiconductor layer faces the first electrode,
and the second semiconductor layer is disposed between the first
and third semiconductor layers.
15. The solar cell according to claim 14, wherein the substrate is
formed of glass, the first electrode is formed of one of tin oxide
and zinc oxide, and the second electrode is formed of an opaque
metallic material.
16. The solar cell according to claim 14, further comprising a
reflective layer disposed between the third semiconductor layer and
the second electrode.
17. The solar cell according to claim 16, wherein the reflective
layer is formed of zinc oxide.
18. The solar cell according to claim 13, wherein each of the
plurality of pillars includes one of circular shape, an oval shape
and a cross shape.
19. The solar cell according to claim 13, wherein each of the
plurality of pillars has a cross shape having a first axis and a
second axis, and further comprising a connecting line connecting
one end of the first axis of the cross shape and ends of the second
axis of the cross shape has a curved shape.
20. The solar cell according to claim 13, wherein the plurality of
pillars are formed of the same material as the substrate.
21. The solar cell according to claim 13, wherein the plurality of
pillars are arranged in a first column and a second column, and
wherein the pillars in the first column and the pillars in the
second columns are alternately arranged.
22. A method of fabricating a solar cell, comprising: forming a
plurality of pillars on a surface of the substrate; forming a first
electrode on the surface of the substrate having the plurality of
pillars; forming a semiconductor layer on the first electrode,
wherein a surface area of the semiconductor layer is greater than a
surface area of the substrate; and forming a second electrode over
the semiconductor layer.
23. The method according to claim 22, wherein the step of forming
the plurality of pillars includes etching portions of the surface
of the substrate such that each of the plurality of pillars
corresponds to a portion between adjacent etched portions of the
surface of the substrate.
24. The method according to claim 23, wherein the step of etching
the portions of the surface of the substrate includes: forming a
plurality of etching mask patterns on the surface of the substrate,
each of the plurality of etching mask patterns corresponding to
each of the plurality of pillars; and etching the portions of the
surface of the substrate using the plurality of etching mask
patterns as an etching mask.
25. The method according to claim 24, wherein the plurality of
etching mask patterns are formed of one of a photosensitive
material and a dry film resist.
26. The method according to claim 24, wherein the step of etching
the portions of the surface of the substrate is performed by a
sandblasting method.
27. The method according to claim 23, wherein the step of etching
the portions of the surface of the substrate includes: forming a
paste pattern having a plurality of openings, wherein a material of
the paste pattern has a reaction with a material of the substrate
to form a reaction portion in the substrate under the paste
pattern, and wherein each of the plurality of pillars corresponds
to each of the plurality of openings; and removing the reaction
portion and the paste pattern.
28. The method according to claim 22, wherein the step of forming
the semiconductor layer includes forming a first semiconductor
layer of a positive type impurity-doped semiconductor material
facing the plurality of pillars, forming a second semiconductor
layer of an intrinsic semiconductor material on the first
semiconductor layer, and forming a third semiconductor layer of a
negative type impurity-doped semiconductor material on the second
semiconductor layer.
29. The method according to claim 28, further comprising forming a
reflective layer between the third semiconductor layer and the
second electrode.
Description
TECHNICAL FIELD
[0001] The present invention relates to a solar cell, and more
particularly, to a solar cell having an improved light absorbing
efficiency and a method of fabricating the solar cell.
BACKGROUND ART
[0002] For response to exhaustion of fossil fuel and preventing
environmental pollution, a clean energy source, e.g., solar energy,
has been come into the spotlight. Particularly, the solar cell for
converting solar energy into electric energy has been developed
rapidly. The solar cell may be divided into a solar thermal cell
and a photovoltaic solar cell. The solar thermal cell generates
steam for rotating a turbine using solar thermal energy, while the
photovoltaic solar cell converts solar photons into electric energy
using semiconductors.
[0003] Among these solar cells, the photovoltaic solar cell, which
absorbs light and converts the light into electric energy using an
electron of a positive (P) type semiconductor and a hole of a
negative (N) type semiconductor, is developed widely. Hereinafter,
the photovoltaic solar cell is referred to as a solar cell.
[0004] The solar cell using the semiconductors has the
substantially same structure as PN junction diode. When light is
irradiated on a portion between the P type semiconductor and the N
type semiconductor, the electron and the hole are induced in the
semiconductors due to light energy. Generally, when light having
energy smaller than band gap energy of the semiconductor is
irradiated, the hole and the electron has a weak interaction. On
the other hand, when light having energy greater than band gap
energy of the semiconductor is irradiated, the electron in a
covalent bond is exited to form an electron-hole pair as a carrier.
The carrier generated by light has a steady-state by recombination.
The electron and the hole, which are generated by light, are
transferred into the N type semiconductor and the P type
semiconductor, respectively, by an inside electric field.
Accordingly, the electron and the hole are concentrated on facing
electrodes, respectively, to be used as a power.
[0005] On the other hand, a thin film of the semiconductor is
formed by one of a vapor phase growth method, a spray pyrolysis
method, a zone melting re-crystallization method, a solid phase
crystallization method, and so on. The zone melting
re-crystallization method and the solid phase crystallization
method have a relatively high efficiency. However, since they have
a high process temperature, a substrate of glass or metallic
material can not be available. They require a substrate having a
high heat stability such that production costs increases. To meet
requirements in production costs, an amorphous silicon thin film or
a polycrystalline compound thin film are deposited by the vapor
phase growth method or the spray pyrolysis method. However, they
have poor efficiency, for example, less than about 10%.
Accordingly, it is required to study a method of fabricating a
solar cell having high efficiency and being available on a glass
substrate.
[0006] FIG. 1 is a cross-sectional view of the related art solar
cell. Referring to FIG. 1, the solar cell 10 includes a substrate
12 and a transparent conductive oxide electrode 14, a P type
semiconductor layer 16, an intrinsic semiconductor layer 18, an N
type semiconductor layer 20 and a metal electrode 22 stacked on the
substrate 12.
[0007] The related art solar cell has a flat shape. Accordingly,
when the intrinsic semiconductor as an active layer absorbs light
through the substrate and the transparent conductive oxide
electrode to generate an electrode-hole pair, the intrinsic
semiconductor should be formed to be thick or a dual cell having a
laminated junction structure, for example, a tandem structure, is
required for increasing an amount of absorbed light.
DISCLOSURE OF INVENTION
Technical Problem
[0008] As mentioned above, to increase an amount of light absorbed
by the intrinsic semiconductor layer as an active layer, there are
some cases. For example, the solar cell has a thicker intrinsic
semiconductor layer. However, it causes problems of increase of
production costs and production time. On the other hand, the solar
cell having an intrinsic semiconductor layer as a dual cell, which
has a laminated junction structure, is provided. However, it causes
problems of increase of production costs and production time, and
there is increased possibility of deterioration.
Technical Solution
[0009] Accordingly, embodiments of the invention is directed to a
solar cell and a method of fabricating the same that substantially
obviate one or more of the problems due to limitations and
disadvantages of the related art are described.
[0010] An object of the embodiments of the invention is to provide
a solar cell having an intrinsic semiconductor layer as an active
layer, which absorbs increased amount of light, and a method of
fabricating the solar cell.
[0011] To achieve these and other advantages and in accordance with
the purpose of embodiments of the invention, as embodied and
broadly described, a solar cell includes a first electrode on a
substrate; a plurality of pillars on the first electrode; a
semiconductor layer on the first electrode, wherein a surface area
of the semiconductor layer is greater than a surface area of the
first electrode; and a second electrode over the semiconductor
layer.
[0012] In another aspect, a method of fabricating a solar cell
includes forming a first electrode on a substrate; forming a
plurality of pillars on the first electrode; forming a
semiconductor layer on the first electrode, wherein a surface area
of the semiconductor layer is greater than a surface area of the
first electrode; and forming a second electrode over the
semiconductor layer.
[0013] In another aspect, a solar cell includes a plurality of
pillars on a surface of a substrate; a first electrode on the
surface of the substrate having the plurality of pillars; a
semiconductor layer on the first electrode, wherein a surface area
of the semiconductor layer is greater than a surface area of the
substrate; and a second electrode over the semiconductor layer.
[0014] In another aspect, a method of fabricating a solar cell
includes forming a plurality of pillars on a surface of the
substrate; forming a first electrode on the surface of the
substrate having the plurality of pillars; forming a semiconductor
layer on the first electrode, wherein a surface area of the
semiconductor layer is greater than a surface area of the
substrate; and forming a second electrode over the semiconductor
layer.
ADVANTAGEOUS EFFECTS
[0015] In a solar cell and a method of fabricating the same
according to the present invention, there is a plurality of pillars
that forms a step difference. Since a semiconductor layer, for
example, an intrinsic semiconductor layer, is formed on the
plurality of pillars, the semiconductor layer has a step difference
due to the step difference. As a result, a surface area of the
semiconductor layer is greater than a surface area of a layer, for
example, a substrate under the semiconductor layer, having an even
surface. Accordingly, the semiconductor can absorb an increased
amount of light, and the solar cell can provide an increased amount
of electromotive force.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are included to provide a
further understanding of embodiments of the invention and are
incorporated in and constitute a part of this specification,
illustrate embodiments of the invention and together with the
description serve to explain the principles of embodiments of the
invention. In the drawings:
[0017] FIG. 1 is a cross-sectional view of the related art solar
cell;
[0018] FIG. 2 is a cross-sectional view of a solar cell according
to a first embodiment of the present invention;
[0019] FIG. 3 is a plan view of a solar cell according to a first
embodiment of the present invention;
[0020] FIGS. 4 and 5 are cross-sectional views showing a
fabricating process of a solar cell according to a first embodiment
of the present invention;
[0021] FIG. 6 is a plan view of a solar cell according to a second
embodiment of the present invention;
[0022] FIG. 7 is a cross-sectional view of a solar cell according
to a third embodiment of the present invention;
[0023] FIGS. 8 to 11 are cross-sectional views showing a
fabricating process of a solar cell according to a third embodiment
of the present invention;
[0024] FIGS. 12 to 14 are plan views of a pillar in a solar cell
according to third, fourth and fifth embodiments of the present
invention, respectively;
[0025] FIG. 15 is a schematic view showing a sandblasting process
according to the present invention; and
[0026] FIGS. 16 and 17 are cross-sectional views showing a
fabricating process of a solar cell using a paste according to the
present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0027] FIG. 2 is a cross-sectional view of a solar cell according
to a first embodiment of the present invention, FIG. 3 is a plan
view of a solar cell according to a first embodiment of the present
invention, and FIGS. 4 and 5 are cross-sectional views showing a
fabricating process of a solar cell according to a first embodiment
of the present invention.
[0028] Referring to FIG. 2, a solar cell 100 includes a substrate
112, a first electrode 114, a plurality of pillars 130, a first
semiconductor layer 116, an intrinsic semiconductor layer 118, a
second semiconductor layer 120, a reflective layer 140 and a second
electrode 122. The substrate 112 may be formed of transparent glass
and have an insulating property. The first electrode 114 may be
formed of a transparent conductive oxide material, for example,
indium-tin-oxide (ITO) or indium-zinc-oxide (IZO) and disposed on
the substrate 112. The plurality of pillars 130 have a cylinder
shape and are disposed on the first electrode 114. The first
semiconductor layer 116 has a positive (P) type and formed on the
first electrode 114 and the plurality of pillars 130. Namely, a P
type impurity is doped into the first semiconductor layer 116. The
intrinsic semiconductor layer 118 functions as an active layer and
is disposed on the first semiconductor layer 116. Namely, no
impurity is doped into the intrinsic semiconductor layer 118. Since
the pillars 130 protrude from the first electrode 114, not only the
first semiconductor layer 116 but also the intrinsic semiconductor
layer 118 has a step difference. The intrinsic semiconductor layer
118 has a concave portion and a convex portion. The convex portion
corresponds to each of the pillars 130, and the concave portion
disposed between adjacent convex portions. Namely, the substrate
112 and the first electrode 114 have an even surface, while the
intrinsic semiconductor layer 118 has an uneven surface.
Accordingly, a surface area of the intrinsic semiconductor layer
118 is greater than that of the first electrode 114 and the
substrate 112. Since the intrinsic semiconductor layer 118 has an
increased surface area, an amount of light absorbed by the
intrinsic semiconductor layer 118 increases. Accordingly, the solar
cell can provide an increased amount of electromotive force. The
second semiconductor layer 120 has a negative (N) type and is
disposed on the intrinsic semiconductor layer 118. Namely, an N
type impurity is doped into the second semiconductor layer 120. The
reflective layer 140 is disposed on the second semiconductor layer
120, and the second electrode 122 formed of a metallic material is
disposed on the reflective layer 140.
[0029] The first electrode 114 is formed on a first surface of the
substrate 112. Light is incident on a second surface, which is
opposite to the first surface, of the substrate 112 and transferred
to the first electrode 114. Light passing through the substrate 112
is incident on the intrinsic semiconductor layer 118 through the
first electrode 114 and the first semiconductor layer 116. The
first electrode 114 is formed to obtain an ohmic contact with the
first semiconductor layer 116. Carrier generated in the intrinsic
semiconductor layer 118 by light is induced into the first
electrode 114 by the first semiconductor layer 116. As mentioned
above, the first semiconductor layer 116 has the P type. The
intrinsic semiconductor layer 118 as the active layer absorbs light
to generate the carrier. Namely, the intrinsic semiconductor layer
118 is formed of an intrinsic semiconductor material. The carrier
generated in the intrinsic semiconductor layer 118 is induced into
the second electrode 120 by the second semiconductor layer 120. As
mentioned above, the second electrode 120 has the N type. The
reflective layer 140 reflects the light, which is incident through
the substrate 112, such that light is incident again on the
intrinsic semiconductor layer 118. A line (not shown) is connected
to the second electrode 122 to obtain an electromotive force.
[0030] Referring to FIG. 3, the plurality of pillars 130 having a
cylinder shape are disposed on the first electrode 114 (of FIG. 2)
of a transparent conductive oxide material. A distance between two
adjacent pillars 130 is determined depending on a respective
thickness of various layers stacked over the pillars 130. The
pillars 130 is formed to maximize a surface area of the intrinsic
semiconductor 118 (of FIG. 2) exposed to light. Each of the pillars
130 may have different cross-sectional shape and different
arrangement than that of FIG. 2. For example, referring to FIG. 6
showing a plan view of a solar cell according to a second
embodiment of the present invention, the pillars 230 may have a
cross shape in plan. In the cross shape pillar 230, a connecting
line between one end of one axis and ends of the other axis has a
curved shape 232. Referring back to FIG. 3, the pillars 130 have an
oval shape of a major axis 132 and a minor axis 134. The pillars
130 are arranged to be spaced apart from each other by a
pre-determined space. The pillar 130 in a second column 138 is
located to correspond to a space between adjacent pillars 130 in a
first column 136. Namely, the pillars 130 in the first column 136
and the pillars 130 in the second columns 138 are alternately
arranged.
[0031] A method of fabricating a solar cell according to a first
embodiment of the present invention is explained with reference to
FIGS. 4 and 5. Referring to FIG. 4, a first electrode 114 is formed
on a substrate 112 by depositing a transparent conductive material.
For example, the transparent conductive material is deposited by a
chemical vapor deposition (CVD) method using tin oxide (SnO2) or
zinc oxide (ZnO). Next, a silicon oxide (SiO2) layer (not shown)
having a transparent property is deposited on the first electrode
114. Then, the silicon oxide layer (not shown) is patterned by a
photolithography to form a plurality of pillars 130. The pillars
130 may be formed of silicon nitride (SiNx) or photoresist. Both
silicon nitride (SiNx) and photoresist have a transparent property.
To maximize a surface area exposed to light of the intrinsic
semiconductor layer (not shown), the pillars 130 is formed of a
transparent material having a high optical transmittance. Moreover,
the pillars 130 are arranged to have compact formation.
[0032] Referring to FIG. 5, a first semiconductor layer 116 is
formed on the first electrode 114 including the pillars 130 by
depositing a P type semiconductor material, where P type impurities
are doped, using a plasma enhanced chemical vapor deposition
(PECVD) method. The first semiconductor layer 116 has a step due to
the pillars 130.
[0033] Next, an intrinsic semiconductor layer 118 is formed on the
first semiconductor layer 116 by depositing an intrinsic
semiconductor material where no impurity is doped. Since the first
semiconductor layer 116 has a step, the intrinsic semiconductor
layer 118 also has a step. Accordingly, a surface area of the
intrinsic semiconductor layer 118 increases. Next, a second
semiconductor layer 120 is formed on the intrinsic semiconductor
layer 118 by depositing an N type semiconductor material where N
type impurities are doped. Next, a reflective layer 140 is formed
on the second semiconductor layer 120 by depositing a reflective
material, for example, zinc oxide (ZnO). Although not shown, a
second electrode is formed on the reflective layer 140. The second
electrode is formed an opaque metallic material, for example,
aluminum (Al).
[0034] The substrate 112, the first electrode 114 and the
reflective layer 140 is treated with a texturing process to have
trapping properties for light. By the texturing process, most of
light, which is incident on the substrate 112, is absorbed onto the
intrinsic semiconductor layer 118. Namely, the texturing process
prevents light being flowed off outside of the solar cell. In more
detail, light passing through the substrate 112 is trapped between
the first electrode 114 and the reflective layer 140. The trapped
light is absorbed onto the intrinsic semiconductor layer 118.
[0035] The intrinsic semiconductor layer 118 absorbs light directly
incident to the intrinsic semiconductor layer 118 through the
substrate 112 and reflected on the reflective layer 140 where the
texturing process is performed. Since the intrinsic semiconductor
layer 118 has an increasing surface area due to the pillars 130,
efficiency of generating an electron-hole pair is improved.
Compared with the intrinsic semiconductor layer 118 in related art
solar cell, the intrinsic semiconductor layer 118 in the solar cell
of the present invention has an increasing surface area with the
same cross-sectional area and the same thickness. Accordingly, the
solar cell has improved efficiency.
MODE FOR THE INVENTION
[0036] FIG. 7 is a cross-sectional view of a solar cell according
to a third embodiment of the present invention, and FIGS. 8 to 11
are cross-sectional views showing a fabricating process of a solar
cell according to a third embodiment of the present invention.
[0037] Referring to FIG. 7, a solar cell 300 includes a substrate
312 having a plurality of pillars 360, a first electrode 314, a
first semiconductor layer 316, an intrinsic semiconductor layer
318, a second semiconductor layer 320, a reflective layer 340 and a
second electrode 322. The plurality of pillars 360 are formed by
etching portions of substrate 312 to protrude from a first surface
of the substrate 312. Since the pillars 360 protrude from the
substrate 312, not only the first electrode 314 and the first
semiconductor layer 316 but also the intrinsic semiconductor layer
318 has a step difference. The intrinsic semiconductor layer 318
has a concave portion and a convex portion. The convex portion
corresponds to each of the pillars 360, and the concave portion
disposed between adjacent convex portions. Namely, the substrate
312 has an even surface, while the intrinsic semiconductor layer
318 has an uneven surface. Accordingly, a surface area of the
intrinsic semiconductor layer 318 is greater than that of the
substrate 312.
[0038] The substrate 312 may be formed of transparent glass and
have an insulating property. The first electrode 314 may be formed
of a transparent conductive oxide material, for example,
indium-tin-oxide (ITO) or indium-zinc-oxide (IZO) and disposed on
the substrate 312. The first semiconductor layer 316 has a positive
(P) type and formed on the first electrode 314. The intrinsic
semiconductor layer 318 functions as an active layer and is
disposed on the first semiconductor layer 316. The second
semiconductor layer 320 has a negative (N) type and is disposed on
the second semiconductor layer 320. The reflective layer 340 is
disposed on the second semiconductor layer 320, and the second
electrode 322 formed of a metallic material is disposed on the
reflective layer 340. Since the plurality of pillars 360 is formed
by etching portions of the substrate 312, a fabricating process is
simplified with compared to that of the first embodiment. Because
the intrinsic semiconductor layer 318 has a step due to the pillars
360, the intrinsic semiconductor layer 318 has an increasing
surface area.
[0039] A method of fabricating the solar cell according to the
second embodiment is explained with reference to FIGS. 8 to 11.
Referring to FIG. 8, a photosensitive material layer 313 is formed
on a first surface of a substrate 312. Next, referring to FIG. 9, a
plurality of photosensitive material patterns 315 are formed on the
first surface of the substrate 312. Each of the photosensitive
material patterns 315 has an island shape.
[0040] Referring to FIG. 10, the substrate 312 is patterned using
the plurality of photosensitive material patterns 315 (of FIG. 9)
as a pattering mask by a sandblasting process to form a plurality
of pillars 360. The pillars 360 correspond to the photosensitive
material patterns 315 (of FIG. 9). Referring to FIGS. 12 to 14
showing various shapes of the pillars in plan, the plan view of the
pillars 360 has one of circular shape 360a in FIG. 12, an oval
shape 360b in FIG. 13 and a cross shape 360c in FIG. 14. In FIGS.
12 to 14, the pillars 360 are arranged in a matrix shape. However,
the pillars 360 may be arranged in other shape. For example, as
shown in FIG. 3, the pillar in a second virtual line is located to
correspond to a space between two adjacent pillars in a first
virtual line.
[0041] Referring to FIG. 15 showing a sandblasting process, a
sandblaster 362 having a nozzle 362a is disposed over the substrate
including the photosensitive material patterns 315. Abrasive
particles 364 of aluminum oxide (Al2O3) are sprayed onto the
substrate 312 through the nozzle 362a. Portions of the substrate
exposed by the photosensitive material patterns 315 are etched by
the abrasive particles 364 such that each of the pillars 160 are
formed under each of the photosensitive material patterns 315.
Namely, the substrate 312 is etched using the photosensitive
material patterns 315 as an etching mask. Instead of the
photosensitive material patterns 315, a dry film resist (DFR) may
be laminated on the substrate 312. The DFR is exposed using a mask
(not shown) and developed to form a plurality of DFR patterns. The
DFR patterns function as an etching mask for the substrate 312.
[0042] Next, referring to FIG. 11, a first electrode 314 is formed
on a substrate 312 having the pillars 360 by depositing a
transparent conductive material. For example, the transparent
conductive material is deposited by a chemical vapor deposition
(CVD) method using tin oxide (SnO2) or zinc oxide (ZnO). A first
semiconductor layer 316 is formed on the first electrode 314 by
depositing a P type semiconductor material, where P type impurities
are doped, using a plasma enhanced chemical vapor deposition
(PECVD) method. The first semiconductor layer 316 has a step due to
the pillars 130. Next, an intrinsic semiconductor layer 318 is
formed on the first semiconductor layer 316 by depositing an
intrinsic semiconductor material where no impurity is doped. Since
the first semiconductor layer 316 has a step, the intrinsic
semiconductor layer 318 also has a step. Accordingly, a surface
area of the intrinsic semiconductor layer 318 increases. Next, a
second semiconductor layer 320 is formed on the intrinsic
semiconductor layer 318 by depositing an N type semiconductor
material where N type impurities are doped. Next, a reflective
layer 340 is formed on the second semiconductor layer 320 by
depositing a reflective material, for example, zinc oxide (ZnO).
Although not shown, a second electrode 322 (of FIG. 7) is formed on
the reflective layer 340. The second electrode 322 (of FIG. 7) is
formed an opaque metallic material, for example, aluminum (Al).
[0043] FIGS. 16 and 17 are cross-sectional views showing a
fabricating process of a solar cell using a paste according to the
present invention. Referring to FIG. 16, a paste pattern 470 having
a gel state is formed on a substrate 412 by a screen printing
method. The paste pattern 470 has a plurality of openings. Next,
referring to FIG. 17, a material of the paste pattern 470 has a
reaction with the substrate 412 of glass to form a reaction portion
472. Namely, a portion 470 under the paste pattern 470 is altered
by the reaction with the material of the paste pattern 470 such
that the reaction portion 472 of the substrate 412 is disposed
under the paste pattern 470. The reaction portion 472 has a
different property than other portions of the substrate 312.
Although not shown, the reaction portion 472 and the paste pattern
470 are removed to form a plurality of pillars. Since the reaction
portion 472 under the paste pattern 470 is removed, each of the
plurality of pillars corresponds to each of the plurality of
openings. Moreover, a first electrode, a first semiconductor layer,
an intrinsic semiconductor layer, a second semiconductor layer, a
reflective layer and a second electrode are stacked on the
substrate 412 having the pillars.
[0044] It will be apparent to those skilled in the art that various
modifications and variations can be made in the apparatus having an
edge frame without departing from the spirit or scope of the
invention. Thus, it is intended that the present invention covers
the modifications and variations of this invention provided they
come within the scope of the appended claims and their
equivalents.
INDUSTRIAL APPLICABILITY
[0045] In the present invention, a solar cell has improved ability
because a semiconductor layer of the solar cell has an increased
surface area. The solar cell is available as an energy source
without problems, for example, environment pollution.
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